Signaling apparatus



Patented June 11, 1946 SIGNALING APPARATUS John S. Leigh, Haddonfield, N. J and Alexander Murdoch, Jr., Philadelphia, Pa., assignors to Radio Corporation of America, a corporation of Delaware Application October 30, 1942, Serial No. 463,860

Claims.

This invention relates to signaling apparatus, and more particularly to electro-acoustic transducers of the magnetostrictive type used especially in submarine signaling.

In submarine signaling apparatus employing magnetostrictive projectors or transducers, it is customary to employ master oscillator-power amplifier driver units. One of the diiiiculties encountered with such drivlng units is that the frequency drifts, thereby impairing the efliciency of conversion of the supersonic electrical energy into pressure waves in the water.

The primary object of our present invention is to provide improved signaling apparatus of the type indicated which will not ,be' subject to. the aforementioned disadvantage.

More particularly, it is an object of our present invention to provide an improved underwater sound system in which the freque cy of the system will not drift.

Another object of our present invention is to provide, in submarine signaling apparatus, an improved system for driving the magnetostrictive projector unit such that the frequency of the system will be controlled essentially by the magnetostrictive activity frequency of the projector unit during operation.

A further object of our present invention is to provide an improved submarine signaling apparatus as above set forth which is relatively simple in construction, inexpensive in cost, and highly efiicient in use.

In accordance with this invention, we provide a multi-stage amplifier for driving the magnetostrictive projector. A feedback path is provided by means of which energy derived from the moving or vibrating diaphragm, in response to energy delivered thereto by the amplifier, is fed back to the amplifier. Thus, there is formed an oscillator having as its charac'tmfi'e th'efireque'ncy by the magnetostrictive activity frequency of the projector unit or transducer.

The novel features that we consider characteristic of our invention are set forth With particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawings, in which Figure 1 is a longitudinal central sectional view of a transducer or projector unit formed according to our invention,

Figure 2 is a sectional view taken on the line IIII of Figure 1 and looking in the direction of the appended arrows, and

Figure 3 is a wiring diagram of the electrical circuit used in connection with our invention.

Referring more particularly to the drawings, wherein similar reference characters indicate corresponding parts throughout, there. is shown, in Figs. 1 and 2, an open-ended casing I over the the'open end of which is secured a magnetic diaphragm 3. The diaphragm 3 is preferably provided with a thin-circumferential portion 5 at which it is secured to the casing l whereby the thicker, central portion thereof maybe moved .substantially as a'wholewSecured tothe dia phragm 3 in any suitable manner are two sets of magnetostrictive elements! and 9 which may be slotted, nickel tubes, for example. The tubes .or elements I, which greatly exceed in number the number of tubes 9, are secured to the diaphragm 3 over a'relatively inner or central portion thereof, and the tubular elements 9 are secured to the diaphragm over a relatively outer area of the diaphragm, so that the tubes 9 are located on a greater radius than are any of the tubes 1 and the tubes 9 surround or are disposed about the tubes 1.

Within the casing I are two sp ced plates l having aligned openings through which the tubes 1 and 9 extend. Each of the inner magnetostrictive tubes 1 is surrounded by a separate coil or winding l3, and each of the outer magnetostrictive tubes 9 is surrounded by a separate coil l5. The coils l3 and I 5 are all disposed between the two spaced plates I I, as clearly shown in Fig. l, and are preferably serially connected. However, successive coils l5 are wound in opposite directions so that, only alternate coils 15 are wound in the same direction. This has the effect of avoiding magnetic coupling between the coils 5 and the coils l3. A shield H of copper or other suitable material is placed around the magnetostrictive tubes 1 and their windings l3, as clearly shown in Fig. 2, to shield the windings l5 electrostatically from the windings l3.

In operation, suitable signal currents are supplied to the windings l3 and the magnetic fields set up thereby cause the tubes 7 to become active magnetostrictively whereby to effect movement of the diaphragm 3. On the other hand, movement of the diaphragm will cause the magnetostrictive tubes to move with it, and therefore will induce signal currents in the coils or windings in well known manner.

An amplifier suitable for driving a projector or transducer unit as above described is shown in Fig. 3. This comprises a single-ended, two stage amplifier of the vacuum tube type having a beam type tube I9 (for example, an RCA 807) in the first stage and a pair of triodes 2| (for example, RCA 81ls) in the second stage. The cathode 23 of the tube I9 is connected to ground through a resistor R1 which is shunted by a bypass capacitor C1. The grid 25 of the tube I9 is connected to ground through the usual shunt connected grid leak resistor R2 and grid condenser C2 in series with a choke coil L1. Plate current is supplied to the plate 2'! of the tube I9 from a suitable source 3| through a dropping resistor R3 and a choke coil L2, the screen grid 29 of the tube 9 being also connected to the potential source 3| through the dropping resistor R3 and an additional dropping resistor R4. A capacitor C3 in the plate circuit of the tube I9 serves as a D.-C. stopping capacitor, and a pair of capacitors C4 and C5 connected between the resistor R4 and ground serve as R.-F. bypass capacitors.

The output of the amplifier tube I9 is coupled to the tubes 2|, which constitute power amplifiers, by a fixed capacitor C6 and a variometer L3,

the capacitor C5 and variometer L3 constituting a resonant load for the plate circuit of the tube I9. By adjustment of the variometer L3, the tunable load in the output of the tube I9 may be tuned either to resonance or cit-resonance, and in this way, the voltage supplied to the grids of the tubes 2| is controlled, so as to obtain the desired output from the second stage of the amplifier.

The grid circuit of the tubes 2| includes an R..-F. choke coil L4 in series with an ammeter 33 and a dropping resistor R5 which is preferably variable. The resistor R5 may be connected through a keying switch 35 either directly to ground, or to ground through a battery 31 which is arranged to provide a negative bias on the grids of the tubes 2|. When the switch 35 is in the lower position for connecting resistor R5 directly to ground, signal potential will be applied to the grids of the tubes 2| from "the output of the tube I9 to operate the tubes 2|. when the switch 35 is thrown to the upper position to connect the resistor R5 to the battery 31, the latter will apply to the grids of the tubes 2| a negative potential below cut-off, so that the signal voltage will not operate the amplifiers 2|.

A capacitor C7 between the variometer L3 and the grids of the tubes 2| serves as a D.-C. stopping capacitor, and a capacitor C8 connected between the choke L4 and ground serves as an R.-F. by-

pass capacitor, as do also a pair of capacitors C9 and C10 connected between the filaments of the two tubes 2| and ground. Plate potentialis supplied to the plates of the tubes 2| from the potential source 3| through an R.-F. chroke coil L5. A grounded capacitor C11 may be provided in shunt with the potential source 3| and also serves as an R.-F bypass capacitor.

The plate circuit of the tubes 2| includesa D.-C. stopping capacitor C12 and has a load consisting of one or more variable capacitors C13 arranged in parallel with the coils or windings I3 which surround the magnetostrictive elements I. In response to signal energy supplied to the coils I3 by the amplifier, the tubes 1 become magnetostrictively active to actuate the diaphragm. turn, the diaphragm moves the tubes 9 to induce currents in the windings or coils I5. The coils I5 are arranged in the grid circuit of the tube i9 and therefore will supply voltage to the grid thereof. A variable capacitor C14 is preferably However,

provided across the windings I5 to provide a tunable system for improving the wave shape of the excitation voltage and for making certain that maximum voltage will be supplied to the grid 25. A capacitor C15 may also be provided in the grid circuit of the tube I9 to serve as a D.-C. stopping capacitor. The windings I3 and I5 are preferably polarized from a suitable D.-C. polarizing source (not shown) through a pair of isolation choke coils 39, and a pair of capacitors C16 and C17 are provided to serve as R.F. bypass capacitors.

It will be clear, from the preceding description, that the coils 13, the coils I5, their associated magnetostrictive tubes or elements 1 and 9, respectively, and the diaphragm 3 constitute a feedback path for the amplifier to render the system an oscillation generator. Energy supplied to the windings I3 from the output of the single-ended power stage 2| activates the magnetostrictive elements 1 to produce vibratory movement of the diaphragm 3. On the other hand, vibratory move ment of the diaphragm 3 causes the attached magnetostrictive elements 9 to move and thereby currents are set up in the windings I5 to produce voltages which are applied to the grid 25 of the tube I9. The magnetostrictive activity frequency of the transducer or projector unit, that is, the natural resonant frequency of the mechanical, vibratory system when it is vibrating, thus controls the frequency of the oscillator and there is no possibility of frequency drift impairing the efficiency of the system.

Although we have shown and described but one embodiment of our invention, it will be apparent to those skilled in the art that .many other forms thereof, as well as changes in the one described, are possible. Thus, any suitable number of magnetostrictive elements 1 and 9 may be employed, ninety-one elements 1 and thirty elements 9 having been shown merely by way of illustration. If desired, the windings |3 and I5 may be arranged in parallel relation instead of being connected serially. Also, various changes may be made within the .amplifier .itself. Many other modifications will, no doubt, readily suggest themselves to those skilled in the art. We therefore desire that our invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. In signaling apparatus, the combination of an electro-acoustic transducer comprising 3. vi-

brator'y diaphragm, a plurality of magnetostrictive elements secured to said diaphragm, a separate winding associated with each of said elements, said elements being actuable in response to signal currents passed through said windings to move said diaphragm and said diaphragm being actuable in response to external forces applied thereto to induce signal currents in said windings, and an electrical signal amplifier having an input circuit and an output circuit, certain of said windings being connected in said out put circuit whereby they are adapted to actuate their associated elements to cause them to effect movement of said diaphragm, and certain other of said windings being connected in said input circuit for feeding back to said amplifier signal energy induced therein in response to movement of said diaphragm, said certain other windings being serially connected and being wound alternately in opposite directions.

2. The invention set forth in claim 1 characterized in that the elements associated with said 5 first named certain windings are secured to a relatively inner portion of said diaphragm, and characterized further in that the elements associated with said second named certain windings are secured to a relatively outer portion of said diaphragm.

3. The invention set forth in claim 1 characterized in that the elements associated with said first named certain windings are secured to an area of said diaphragm which is of smaller radius than the area of said diaphragm to which the elements associated with said second named certain windings are secured.

4. The invention set forth in claim 1 characterized in that the elements associated with said first named certain windings are secured to an area of said diaphragm which is of smaller radius than the area of said diaphragm to which the elements associated with said second named certain windings are secured, and charcterized further in that said last named elements are disposed circumferentially about said first named elements.

5. The invention set forth in claim 1 characterized in that the elements associated with said first named certain windings are secured to an area of said diaphragm which is of smaller radius than the area of said diaphragm to which the elements associated with said second named certain windings are secured, characterized further in that said last named elements are disposed circumferentially about said first named elements, and characterized still further by the addition of electrostatic shielding means around said first named windings whereby to shield said first named windings electrostatically from said second named windingsj r JOHN S. LEIGH. ALEXANDER MURDOCH, JR. 

